"Arigatou" is simply "thanks". When you want to sound more polite, you could say "arigatou gozaimasu". This, accompanied with a small bow (just lower your head slightly), is all that is expected of foreigners.
"Sumimasen" works similarly to "excuse me" in English. Just like the English phrase, "Sumimasen" too can be used in two contexts:
"Ohayou" or the more polite "ohayou gozaimasu" means "good morning". Short-term visitors can just get by with the short and sweet, "Ohayou".
"Hai" signifies "yes" and "iie" "no". A little body language helps. indicating example, the Japanese body language indicating "okay" (typically "yes") is extending the thumb and index finger in a circle with the other three fingers. T
This is a handy phrase for travelers. This is the phrase you should use when you want to ask for something.
Similar to "Noun wo kudasai" but more polite. "I request" is "Onegaishimasu". You could say "water, onegai shimasu"—"water, please". "English, onegaishimasu" means "English, please" in Japanese.
This is especially important for those who have food restrictions. For example, if you are vegetarian, then you could say "fish/meat nashi, onegaishimasu" or "nikusakana nashi, onegaishimasu."
"Gomen nasai" is "sorry". While "sumimasen" also works like a mild apology, "gomen nasai" is preferred when you truly need to apologize.